1. Field of the Invention
The invention relates to short circuit stops for induction machines that restrict relative motion between a paired induction machine component and a brace. More particularly the invention relates to generator short circuits stops and their methods for installation, including replacement during generator retrofitting in service facilities or at field installation sites.
2. Description of the Prior Art
Induction machines, such as generators, have components capable of motion during machine operation. It is often desirable to limit motion range of components. For example, generator stators have a generally annular structure in which is captured a rotor. The generator stator annular structure has an end basket affixed to one end by building bolts having a stack of compressible end washers to allow a limited range of expansion and contraction. In a short circuit event it is desirable to restrain axial and radial movement of the building bolts. The building bolts are restrained by one or more braces that are interposed within the bolt's potential range of motion at a selective gap distance. A stop is interposed between the paired building bolt and brace. The stop may be selectively positioned to set a desired gap or spacing between itself and a paired component, such as a building bolt. Depending on the stop design, the gap may be altered or permanently set.
One type of existing generator stop is a threaded stop stud that is captured within mating female threads formed in the generator brace. The threaded stud is advanced into the brace so that it is selectively positioned proximal to the building bolt or other apparatus component whose motion is intended to be restrained by the stop. The threaded stop stud has a relatively thin diameter compared to its projection length out of the generator bracket, and thus is susceptible to bending during a generator short circuit event. Threaded stop stud replacement requires careful removal of the old stop stud, so as not to damage the corresponding female threads within the generator brace. Damaged female threads require repair before inserting a new threaded stop stud. The threaded stop stud dimensions vary among different generator models and, it may not be possible to ascertain with certainty needed replacement stud dimensions prior to generator disassembly. Thus additional generator down time may be incurred during the repair cycle while service technicians obtain replacement stud parts.
Another type of existing generator stop is an L-shaped bracket, one leg of which is permanently affixed to the generator brace, such as by welding. The other leg of the L-shaped bracket is oriented generally parallel to the brace and functions as the stop surface to restrain the building bolt or other apparatus component. Positioning the L-shaped bracket relative to the building bolt is accomplished by hand, and the bracket is clamped to the brace prior to the welding operation. Different generator configurations require different dimension brackets, and those dimensions may not necessarily be ascertained until the subject generator is removed from service and disassembled for inspection. This in turn requires ordering of L-bracket parts after initial disassembly, and possibly longer generator down time until the appropriate L-brackets are obtained. L-brackets are permanently attached to the generator brace, such as by welding procedures. Subsequent generator rebuilds and/or service may require time-consuming removal of the welded L-brackets, followed by re-welding of replacement brackets to the generator brace.
Thus, a need exists in the art for a short circuit stop for an induction machine, such as a generator, having robust construction that is not easily susceptible to damage in the event of a generator short circuit event.
Another need exists in the art for a short circuit stop capable of field installation without permanent attachment to induction machine components, such as generator braces, that can be selectively installed and uninstalled, preferably without modification of the underlying support components.
Another need exists in the art for a short circuit stop capable of meeting dimensional and configuration requirements of different induction machine designs, directly out of the box or by field fitting, so that the types of short circuit stop spare parts can be minimized in service inventory; or if not available in inventory, preferably quickly fabricated after initial repair disassembly and inspection so as to minimize repair down time.